1. Field of the Invention
The present invention relates generally to thermal barrier coatings (TBC), and more specifically to a fluid reaction surface with a TBC.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine includes a compressor, a combustor, and a turbine. The compressor compresses air and delivers the compressed air to the combustor where the compressed air is mixed with a fuel and burned. The hot gas stream exiting the combustor is passed through the turbine to produce rotary motion and useful work from the engine. The efficiency of the gas turbine engine increases as the hot gas temperature entering the turbine increases. It is desirable to design a turbine to operate at the highest gas flow temperature possible without burning up the turbine parts such as guide vanes and rotary blades. Cooling air has been passed through the upstream stages of the vanes and blades in the turbine in order to cool these parts and allow for higher gas stream temperatures. A ceramic thermal barrier coating (TBC) has also been applied to parts of the vanes and blades that are exposed to the high temperature gas flow in order to protect the airfoil surfaces from the extreme temperature.
Recently, designers of turbine airfoils have tried to apply even thicker TBC to the airfoil surfaces. However, as the thickness of the TBC increases, the ease at which chunks of TBC can break off (spalling) increases. A thicker TBC will allow for higher gas flow temperature without damaging the airfoil surface below the TBC. It is therefore desirable to allow for a thicker TBC without increasing the likelihood that spalling of the TBC will occur.
U.S. Pat. No. 6,551,061 issued to Darolia et al. on Apr. 22, 2003 shows a Process For Forming Micro Cooling Channels Inside a Thermal Barrier Coating System Without Masking Material in which the TBC is formed of a first and a second TBC layer, and in micro cooling channels are formed between adjacent surfaces of the inner TBC and the bond coat to provide cooling to the TBC. The micro cooling channels in this patent do not pass entirely within the TBC layer and do not open onto the TBC surface on which the hot gas stream contacts.
Another patent, U.S. Pat. No. 6,617,003 issued to Lee et al. on Sep. 9, 2003 entitled Directly Cooled Thermal Barrier Coating System shows a TBC applied over a bond coat which is applied over a substrate of an airfoil used in the turbine, where micro channels are formed entirely within the bond coat, within adjacent surfaces between the substrate and the bond coat, between adjacent surfaces of the bond coat and a inner layer of TBC, and wholly within the layer of the inner TBC. However, the micro channels in this patent are formed within the actual bond coat or TBC materials and do not open onto the exposed surface of the TBC on which the hot gas stream contacts.
U.S. Pat. No. 6,761,956 issued to Lee et al. on Jul. 13, 2004 and entitled Ventilated Thermal Barrier Coating shows an airfoil of a turbine having a TBC applied on the airfoil substrate, and cooling holes passing formed within the TBC and passing from the substrate to the surface of the TBC for cooling. The holes are formed within the TBC by laser drilling.
When a TBC is applied to a metal substrate of an airfoil that has cooling holes therein, a mask is applied over the holes before the TBC is applied to prevent the holes from being covered over by the applied TBC. When the TBC has hardened and cooled, the mask is removed, leaving sharp edges on the TBC where the mask was. The surface of the cooling holes under the mask is exposed to the hot gas temperature, and the sharp edges on the TBC can break off in use.
It is therefore an object of the present invention to provide for a TBC that can operate at a higher temperature than the prior art.
It is another object of the present invention to provide for a TBC that is reinforced.
It is an additional object of the present invention to provide cooling for the TBC as well as to provide increased strength to the TBC to reduce spalling.
It is still another object of the present invention to eliminate exposed substrate surfaces around cooling holes due to the masking when a TBC is applied to the substrate.